A laser machining device is a device that reflects laser light emitted from a laser oscillator off a curvature variable mirror, a laser-light reflecting mirror, or other mirrors to irradiate a workpiece with the laser light. Oxygen-free copper has a high heat conductivity, and therefore has been used conventionally for a mirror base material that constitutes the curvature variable mirror or other mirrors. When distortion occurs in the mirror base material described above, a desired beam diameter cannot be obtained. Therefore, there is a need for a mirror base material that prevents the occurrence of distortion.
For example, a variable shape mirror described in Patent Literature 1 uses a metal material such as phosphor bronze as a material of a support spring that couples the variable shape mirror with a support body. This prevents the occurrence of abnormal deformation of such an elastic member.